This invention relates to gas turbine engines and particularly to a cool air system for cooling components in the turbine section and controlling the gap of the lentricular seal.
As is well known, the advent of the high cost of fuel coupled with a need to conserve energy has caused the gas turbine industry to undergo an extensive program to develop engines so as to improve thrust specific fuel consumption (TFSC). To this end the cooling means for the turbine section which typically bleeds air from the compressor section is the concern of this innovation. Historically, the air from the compressor was fed directly into the area of the turbine section to cool its working components and particularly the turbine vanes and blades. Turbine vane and blade cooling has developed in a complex and sophisticated art in and of itself. But suffice it to say for purposes of this invention, that it is necessary to supply a large volume of air to the turbine section particularly to accommodate the high pressure drop incidental to the passage of flow through the multiple internal passages and apertures in the vanes. Obviously, during takeoff, when engine power demand is at its highest peak, the amount of air required is far more than the amount required at a lesser power demand, say during cruise.
To accommodate the difference in demands, we have found that we can conserve on compressor air with a consequential improvement on TSFC by having at least two different ducts connected to the compressor station being bled and one being valve operated and the other being continuous feed but having flow restriction. The flow restriction assures that the amount of air being fed by the continuous feed duct does not increase appreciatively when the valve is closed, since both ducts are fed from the same source.
Additionally, the amount of air selected from the continuous feed duct is sufficient to cool the gas path air only enough to cool the lenticular seal, but yet leaving the mixed air warm enough to close the gap thereof and minimize gas flow leakage, with a consequential additional improvememt in TSFC.